The embodiments described herein relate generally to electric distribution systems and, more particularly, to apparatus for enhancing control of voltage and power factor within electric distribution systems.
Known electric power grids typically include power generation plants, transmission and distribution lines, transformers, and other devices that facilitate electric power transmission, and power delivery. After electric power is generated in the generating plants, it is transmitted for extended distances through the high voltage transmission lines to subtransmission/distribution substations. Transmission lines usually operate at voltage levels between approximately 115 kilovolts (kV) and approximately 765 kV. At the subtransmission/distribution substations, transformers reduce the high voltage at which the power has been transmitted to sub-transmission voltage levels that range from approximately 46 kV to approximately 69 kV, or to distribution voltage levels that range from approximately 12 kV to approximately 34.5 kV. Power is then transmitted through a feeder to an end customer through an electric distribution system, and before it reaches the end customer, the voltage is decreased to approximately 120V/240V by a distribution transformer.
Most known electric distribution systems include a plurality of feeders coupled to the substation transformer. Each feeder includes a plurality of distribution transformers. The feeder may also include at least one capacitor bank, at least one voltage regulator, and at least one distributed generation device, e.g., a diesel generator. A plurality of typically open tie switches, each adjacent to a neighboring substation, define the outer boundaries of the feeder. The feeder is divided into smaller units via disconnect switches, reclosers, sectionalizers, and fuses.
In some known feeders, the voltage decreases between the head of the feeder and the end of line (EOL) customers. Therefore, to maintain voltage within predetermined parameters during peak electric loading periods, including those regions most remote from the feeder head, the power generation plants raise generated voltage and/or adjust the power factor. Alternatively, or in addition to the actions of the generation plants, localized distributed generation devices may be started. These actions require combusting additional fuel resources and increasing the costs of operation, thereby decreasing system efficiency merely to support localized voltage levels and power factors. In other known feeders, local capacitor banks are used to support local voltages. However, such local voltage regulation may require multiple, unnecessary switching to bring the capacitor banks on-line and take them off-line in relatively short time frames. Moreover, such local voltage regulation may not adequately control other operating parameters within the feeders, such as active power losses across the sections from head of the feeders to the EOL customers.